﻿ The Answer to the Cool Maths Trick » Techie Buzz
The Answer to the Cool Maths Trick
By on September 27th, 2007

If you studied hard at school you may remember Algebra well lets do some algebra magic out here to crack the solution for yesterday’s post on how I can figure out your age without you telling me, if you have not read that yet read it first and come back to view the solution.

Assume ‘x’ to be any number that you want it may be a single digit number or a double digit number or a triple digit number. The final outcome would depend on the number of digits you choose so if you choose single digit number the final outcome will be a 3 digit number, for a double digit number the outcome will be a 4 digit number and so on.

Of course a 0 will result in an output of 2 digit number.

Next Step: Multiply it by 2
Output: 2x

Next Step: Add 5 to it
Output: 2x + 5

Next Step: Multiply it by 50
Output: 100x + 250

Let’s Ponder

At this stage it is quite certain that you will always get a result of 250 even if you have chosen 0 as the first age, lets keep the 100x aside for a bit and look at the numbers 1756 and 1757.

Adding up 250 and 1757 results to 2007 and adding up 250 and 1756 results to 2006, that is year lesser than this year.

Now if your birthday hasn’t passed it is quite obvious that your age is that as of 2006 and if it has passed it is that as of 2007. Now the claim that this will only work in 2007 is partly correct. This will work in any year if you change the number 1756 and 1757 to a number that on adding to 250 give you the current year and previous year.

So assuming its 2010 the numbers would be 2010 – 250 = 1760, for those whose birthdays have not yet passed you have subtract one from 1760, so the two numbers to be used in 2010 will be 1759 and 1760.

Example for year 2010

3 x 2 = 6 + 5 = 11 * 50 = 550 + 1759 = 2309 – 1982 = 327

Now the last two numbers is my age in 2010.

You need to use 5 and 50 because the other two numbers 1757 and 1756 add up to give you a result which is the current year or the previous year for those whose birthday’s are not yet passed for the year.

You can use practically any numbers to get the same results that end up in showing you your current age. For example using 6 as the base and 10 as the multiplier the other two numbers that would be used is 1947 and 1946 which is subtracted from the current year by 60.

Converting this logic into a simple algebra expression

Current year = c, basenum = b, multiple = m, x is the number to subract, y is the number to subtract if the birthday has not passed this year

x = c – (b * m)

y = c – (b * m) – 1

Simple isn’t it.

Now the mystery 100x?

What we learnt above is the base of solving the mystery, but the bigger mystery is how can any random number fetch accurate results. That part of the mystery is the 100x formula.

The number you choose does not make and difference, the outcome will always be 100x, so if you choose 2 the outcome would be 200, if you choose 3 the outcome would be 300 and so on.

Lets analyze the trend with the final results.

If you chose 1. Outcome will be 2107
If you chose 2. Outcome will be 2207
If you chose 3. Outcome will be 2307
If you chose 4. Outcome will be 2407
If you chose 5. Outcome will be 2507
If you chose 6. Outcome will be 2607
If you chose 7. Outcome will be 2707
If you chose 8. Outcome will be 2807
If you chose 9. Outcome will be 2907

Now there are two trends out here which we will look at one is that subtracting the 100x output will from the final output will always give you the current year, here is how the simplified formula looks like assuming x is the number you choose and current year is y and z is your final output after doing all the above calculation.

y = z – 100x;

Another trend that you will notice is that since it is multiplying x by 100 the resultant output would be x00 always.

The age guessing trick

When you subtract your birth year from the output you are always left with a output similar to xYY where x is the number you chose and YY is your age, since we already know that 100x will always result in multiples of 100 the subtraction of your birth year is always performed on the current year adding up your age to 100x.

The final formula is assuming z is your birth year

YY = ( ((x * 2) + 5 + 1757) + 100x ) – z;

The result of the formula will always be xYY, where x is the number you chose and YY is your current age.

Simple isn’t it, no wonder there are so many maths fanatics around. I loved solving this trick and it turned out to be a interesting thing after all. Ashish from Technospot.net came very close to the actual formula.

Well do let me know your thoughts on it by adding your valuable comments.

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Author: Keith Dsouza
I am the editor-in-chief and owner of Techie Buzz. I love coding and have contributed to several open source projects in the past. You can know more about me and my projects by visiting my Personal Website. I am also a social networking enthusiast and can be found active on twitter, you can follow Keith on twitter @keithdsouza. You can click on my name to visit my Google+ profile.

Keith Dsouza has written and can be contacted at keith@techie-buzz.com.
• http://www.technospot.net/blogs/ Ashish Mohta

WO…..Didnt knew tha algo was that complex. :) I just solved in a different way :D .

• keith

Yups it was :-), but it looks quite simple in the end.

• http://www.technospot.net/blogs/ Ashish Mohta

Hehe I will be waiting for my \$\$\$ now :D.

• keith

It’s on its way :-)

• mark

how does this work….YY = ( ((x * 2) + 5 + 1757) + 100x ) – z; can somebody plug in the numbers for me….i cant get the number. thank you

• mark

can someone try to plug in the numbers for the YY = ( ((x * 2) + 5 + 1757) + 100x ) – z; i keep getting a wacky answer..thank you

• Kat

Mark,

You need to remember to use Order of operations, you can’t just do the sum straight across.
BIDMAS (or other variations) BEDMAS, BIMDAS (whatever you learnt at school).

Brackets
Indices
Divison
Multiplication